1. Field of the Invention
This invention relates to an optical recording disk having a dye base recording layer.
2. Prior Art
Optical recording disks of the write-once, rewritable and other types have been of great interest as high capacity information bearing media. Among the write-once optical recording disks, those having a recording layer predominantly comprising a dye have the advantage of low cost manufacture because the recording layer can be formed by coating.
There were commonly used optical recording disks of the air-sandwich structure having an air space on a dye base recording layer. Recently disks of the close contact type having a reflective layer in close contact with a recording layer were proposed because they could be reproduced in accordance with the compact disk (CD) standard. See Nikkei Electronics, Jan. 23, 1989, No. 465, page 107; the Functional Dye Department of the Kinki Chemical Society, Mar. 3, 1989, Osaka Science & Technology Center; and Proceedings SPIE--The International Society for Optical Engineering, Vol. 1078, pages 80-87, "Optical Data Storage Topical Meeting", 17-19, January 1989, Los Angels. The optical recording disks of the close contact type are fabricated by forming a dye layer, a reflective layer and a protective layer on a transparent substrate in the described order so that the reflective layer is in close contact with the dye layer, meeting the disk total thickness of 1.2 mm required by the CD standard.
In order that optical recording disks having a dye base recording layer be reproduced by means of a CD player, one proposal uses a gold (Au) reflective layer because the aluminum reflective layer used in conventional CDs has insufficient reflectivity. Although gold has high reflectivity and corrosion resistance, it is expensive. It is thus contemplated to use less expensive metals having reflectivity as high as gold, for example, alloys such as Ag--Cu and Cu--Al alloys.
Optical recording disks using organic dyes in the recording layer are known to contain metal complexes as singlet oxygen quenchers in the recording layer. Some dyes are in the form of metal complexes. Disks having reflective layers of copper and other alloys, however, are less reliable because copper and some metals are reactive with metal complexes as the dye, causing deterioration of the dye and a lowering of signal outputs.